An aqueous coating material is useful as a coating material suitable for natural environmental protection since it is possible to reduce the content of an organic solvent as compared with a solvent type coating material. As a process for producing the aqueous coating material, a process to obtain a water-dispersion by emulsion polymerization of a fluorocopolymer, is known. However, in order to secure the dispersion stability only by an emulsifier, a substantial amount of the emulsifier needs to be used, which causes decrease of the water resistance or weather resistance of a coating film to be obtained. As one of the methods to solve such a problem, it has been proposed to introduce hydrophilic moieties in a copolymer.
For example, Patent Document 1 discloses an invention relating to an aqueous coating composition. It is disclosed that the composition can be obtained by carrying out emulsion polymerization of a fluoroolefin with another monomer by using a fluorocopolymer having a hydrophilic side chain as an emulsifier.
Patent Document 2 discloses an invention of a coating material which is a composition comprising a polymer for fluorinated coating material which contains from 4 to 30 mol % of a carboxylate-containing structure unit in which at least 30% of a carboxyl group is neutralized with ammonia or a tertiary amine, and an aqueous medium containing at least 10 vol % of a hydrophilic medium based on water.
Patent Document 2: U.S. Pat. No. 5,447,982
Patent Document 3: U.S. Pat. No. 5,171,804